1. Field of the Invention
The present invention relates to filtering devices used in combination with compressed air, heavy vehicle braking systems. More particularly, the present invention is directed to a filtering cartridge that is disposed downstream of an air brake compressor and that has a thermal venting capability.
2. Description of the Prior Art
Compressed air systems are used in vehicles to provide and maintain air under pressure to operate vehicle brakes and associated auxiliary air systems. Conventional systems include an air compressor for generating pressurized air and a drying device or air dryer disposed downstream from the compressor for removing entrained liquid from the air. The air dryer includes a desiccant material that removes water vapor from the air as it passes therethrough.
Air brake compressors are typically supplied with oil from the vehicle engine in order to lubricate the bearings and other components of the compressor. However, because oil is difficult to contain, a small portion of the lubricating oil passes into the pressurized air stream exiting the compressor in the form of oil vapor and carbon particles. If air exiting the compressor passes directly to the downstream components, elastomeric seals and seats of the components, as well as the desiccant material housed within the air dryer, can become contaminated with the oil and carbon.
Therefore, some vehicle air brake systems are provided with a filter cartridge located immediately downstream of the compressor. The filter cartridge includes a filter located in a housing. The filter is spring biased against an inlet end of the housing. Air flowing into the filter housing is directed to flow through the filter before it flows out of the housing. The filter causes the oil vapor and carbon particles to coalesce in the filter, thus preventing it from flowing downstream to the operating components of the braking system.
The coalesced oil and carbon has an autoignition temperature of around 400° F. If it ignites within the filter it can cause major damage to the vehicle. U.S. Patent Application Publication No. 2003/0110949 A1 discloses a spin-on filtering cartridge that includes a thermal vent. With the thermal vent, pressure is released from the cartridge upon reaching a threshold temperature.
In the known filter cartridge, a pressure increase due to filter clogging can cause the filter to compress the spring and move away from the inlet end of the housing, allowing air to flow freely around the filter.